Differential adjustment



Sept. 27, 1960 M. F. KAUTZ 7 2,953,929

DIFFERENTIAL ADJUSTMENT Filed Sept. 26, 1958 IN V EN TOR.

M'URRELL F. KAUTZ ATTORNEY/ United States Patent DIFFERENTIAL ADJUSTMENT Murrell F. Kautz, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed Sept. 26, 1958, Ser. No. 763,565

Claims. (Cl. 74-100) This invention is directed to differential adjusting means suitable for use with condition responsive control devices. A common use of differential adjusting mechanisms is in pressure responsive switches.

The objects of the invention is to provide a control device having a differential adjustment that can be calibrated so that an indicating scale will show actual differential in terms of condition value.

The disclosed control device is of the type having a lost motion differential adjustment driving a snap switch that has two stable operating positions. The arrangement is such that the switch will stay in either of these positions until driven to the other. Diiferential is adjusted by changing the extent of lost motion. Such differential adjusting arrangements are old, but were lacking in means for setting the differential indicating scale to read correctly at more than one point. Under some circumstances it is impossible to provide a precalibrated scale that will reasonably match a screw of given pitch or cam of fixed shape in all units of a device to be manufactured in quantity. In the pressure control illustrated, the principal cause of variations for which correction must be made is in the effective spring rates of the pressure sensing diaphragms applied to different devices. According to the invention one of-the abutments in the lost motion connection is in the form of a variable pitch cam that can be adjusted so that a predetermined angular movement will produce a predetermined change in differential of the control device.

In the drawing:

Figure l is an elevation, partly in section, of a pressure control incorporating the invention.

Figure 2 is a perspective view of the instrument shown in Figure 1.

Figure 3 is a plan view of the differential dial.

The pressure actuated switch shown in the drawing has a case 10 open at the front and top and a cover 11 that hooks over the upper rear and the upper and the front edges of case and is held by a screw 12 in an upturned edge at the bottom of the case.

A diaphragm assembly 15 is secured to the bottom of the case 10 by screws 16 and includes a housing 17 within which a cup shaped diaphragm 18 is fitted. A pressure connection 19 is secured to the bottom of the housing 17. An actuator 20 has an enlarged lower end engaging the diaphragm and a portion of small diameter extending through an opening in the bottom of case 10.

A main lever 22 is pivoted in the case 10 on a rod 24 which is supported at its rear end in the back of the case and at its front end in a bracket 25 attached to the bottom of the case. A main calibration screw 27 is threaded in the main lever 22 with its lower end engaging a crater in the top of actuator 20. A control point adjusting spring 28 engages the left end of the main lever 22 and biases it in a clockwise direction to oppose expansion of the diaphragm. The top of spring 28 is in threaded engagement with an indicator member 29 which in turn is threaded to receive an adjusting screw 30. The

2,953,929 Patented Sept. 27, 1960 head of the screw 30 bears on a tab formed in case 10 and an opening (not shown) is provided in cover 11 so that the screw can be adjusted without removing the cover. The indicator 29 has an offset portion 32 that extends through a slot in a scale plate 34 formed as part of case 10. The offset portion 32 prevents rotation of indicator 29 when the screw 30 is adjusted and also cooperates with suitable indicia on scale plate 34 to indicate the pressure at which the control device will be moved to one of its operative positions.

A snap switch 36 having an operating plunger 37 and terminals 38 is secured to the back of case 10 by screws 39. The switch may be of the type shown in McGall 1,960,020. A diiferential lever 42 is pivoted on the rod 24 which also pivotally mounts the main lever 22. The portion of lever 42 to the left of its pivotal axis extends upwardly parallel to the case of the snap switch 36 and operatively engages the switch plunger. A leaf spring 44 engages the differential lever 42 at its upper extremity and biases this lever in a clockwise direction. Intermediate its ends the spring 44 bears on the rod 24 and its right hand end is slotted to lie under the head of a screw 45. Screw 45 which is threaded in case 10 is adjusted so that the bias on lever 42 results in an inward force on the snap switch plunger intermediate the operating and release forces of the switch. Hence, unless another force is applied to the differential lever 42, the switch will remain in either of its operative positions.

The right hand end of differential lever 42 has a portion 42a offset downwardly to lie beneath main lever 22. A screw 48 threaded in the main lever is adapted to engage portion 42:: of lever 42 to drive the lever 42 in a clockwise direction.

The differential lever 42 is driven in a counterclockwise direction by an abutment surface in the form of a cam 50 of variable pitch rotatably mounted on the main lever 22. The cam assembly includes a stud 51 extending through the main lever. A laterally extending bracket 53, a normally flat flexible dial 55 which provides the actual cam surface, and a spacing washer 61 are secured to the upper part of the stud 51. Beneath the main lever 22 the stud carries a friction washer 62 and a spring washer 63 which biases the friction washer toward the main lever. The arrangement is such that the cam assembly will remain in any angular position to which it is adjusted.

As seen in Figure 3, the flexible dial 55 has a central portion 56 that engages the stud, a portion extending radially from the central portion and an arcuate peripheral portion 58 supported at one end by the radial portion. In addition, radially extending ears 59 and 60 are provided to cooperate with an upwardly extending portion 22a of main lever 22 to limit the range of angular adjustment of the cam. The right hand end of the difierential lever 42 is provided with an abutment portion 42b offset upwardly and adapted to engage the upper surface of the dial 55. The extremity of portion 42b also acts as a pointer cooperating with numerals 64, indicative of pressure, on the surface of dial 55.

The bracket 53 is screw threaded at a point overlying the free end of the arcuate portion 58 of the dial 55 to receive a cam adjusting screw 65. The screw is adjusted to deflect the free end of the dial downwardly out of its normal plane so that the cam will have the required slope to produce an actual operating differential in agreement with the differential indicated by the numerals on the dial surface. in manufacture, all dials for a particular type of instrument have the numerals disposed in the same angular relation on the dial surface. As stated above, it has been found that variations in spring rate of the mechanism, particularly of the diaphragm itself, produce rather wide differences from one its; difterentiaL. All: possible variables, are, resolvedxby providing; a,- cam; of, variable slope.

To, calibrate the, differential adjustment, the numeral- 1. is set beneath the pointer provided by extension 42b of, difierential lever, 42 and the screw 48 adjusted to. produce,; an actual. operating, ditierential of one pound per, square inch. Sincethe numeral 1. is located, at a portion ofthe dial that has substantially no deflection when the screw 65is turnedto deflect, the dial, subsequent adjustment of screw 65 will not appreciably afiect this adjustment. The dial isvthen turned. until/the numeral 5,, lies beneath the; lever extension 42b and the screw 65 adjusted to produce an .actual operating differentialof five-poundspersquare inch.

In the illustrative device the, snap switch is of. the

normally. open type sothat atpressuresbeneaththe control range, the spring28 holds the; switch in closed position Hence, the switch will open at the pressure indicatecLonthe scale plate 34. plus the pressure indicated on diaLS-S, andwwill close at the pressure indicatedon scale plate 34.; With this arrangement there is no possibility of the diiferential being adjusted so-wide at any main scale-setting that the switch will not cut in, because differentialis added tothe main adjustment. It will be notedthat difierentialwill be, substantially. unaffected by adjustment of, spring.2 8 because the switchalways cuts mat the same position of the diaphragm regardless of theforce required to move the main lever.

It will be understood that the invention is not limited to diiferential adjustments in which the lost motion adjustment is between two levers. Obviously the lost motion: could, be between any two relative movable members or between a movable member and a stationary portionof the device.

Iclaimas my invention:

1. Acontrol device comprising, a condition responsive element, a control elementthaving two stable operating conditions, a lost motion driving connection betweensaid conditionresponsive element and said control element, said lost motion connectionincluding an adjustableabut: ment consisting of a member rotatable on an axis substantially parallel to the direction of relative movement of the, abutting portions, of the connection, a normally flattsp ringistrip having a. portion extending radially from said;m emb er and an arcuate portion encircling said member and radially spaced therefrom, a plate extending radially from said member and .overlyingthe freeend of the-arcuate portionof said strip, a screw in threaded engagement with said plate and engaging the free end of, the arcuate portion of said strip and adjustable. to

deform the arcuate portion of said strip into helical form providingan abutment surface of adjustablepi-tch, and an indicator of condition value positioned in accordance with-theangularly adjusted position of said member.

2, A control device comprising, a condition responsive element, a control element having two stable operating conditions, a lost motion driving connection between said condition responsive element and said control element, said lost motion connection comprising abutment means rotatable onan axis substantially parallel to the direction of relative movement, said. abutment means having a helical abutment surface of variable pitch, means for changing the pitch angle, and an indicator of condition value positioned in accordance with the angularly adjusted-position of said abutment means.

3. A control device comprising, a condition responsive element, a control element having two stable operating conditions, a lost motion driving connection between said conditionresponsive element and said control element, saidlost motion drive including an adjustable abutment comprisinga normally flat arcuate spring strip angularly adjustable on the axis of the arc, means for adjusting the relative axial spacing of the two ends of said strip, and an indicator of condition value positioned in accordance with the angularly adjusted position of said strip.

4. A control device comprising, a condition responsive element, a control element having two stable operating conditions, a driving connection between said elements, means for adjusting; andindicating the condition values at which said control element is moved to both of its operating conditions, said driving connection including. lost motion means for varying the relation of thetwo operating conditions, said' lost motion means including an adjustable. abutmentcomprising a normally fiat arcuate spring strip angularly adjustable on the axis of the are, means for adjusting the-relative axial spacing of the two ends of the strip, and an indicator of condition value positioned in accordance with the angularly adjusted position of saidstrip.

5. A control device. comprising, first andvsecond' coaxiallv-pivotedlevers, condition sensing means, acting on said first'lever to position said lever in accordance with conditiorrvalue, a control element actuated between .two operative positions by said second. lever, cooperating abutmentson said.levers to cause said second lever to move with said first lever,'one, of saidabutments comprisingan arcuate strip carried. at one end by a member rotatable on an axis spaced from and normal to the pivotal axis ofzsaid levers, means for varying the axial deflectioniof the other. end of said strip, and indicia ofcondition value rotatable with said strip.

6. A controLdevice comprising, first and second coaxially pivoted levers, condition sensing means acting on said first lever to position saidlever in accordance with condition value, a snap switchactuated by said second lever, cooperatingabutments on said levers to cause said second lever to move with said first lever, one of' said abutments comprising an arcuate strip carried at one end by a member rotatableon one of said levers on an axis normal to and spaced from the axis of said levers, means for, determiningthe axial deflection of the other end of said strip, and indicia of condition value on said'strip cooperating with an index on said one lever to indicate operatng differential.

7. A' control device comprising, a frame, first and second .levers coaxially pivoted on said frame, anexpansible chamber acting on said first'lever; a spring acting between said frame and said first lever to oppose expansion of said chamber, indicia associated with said spring to indicate the control point of the device in terms of condition value, a snap switch actuated by said second'lever, cooperating abutments on said" levers to cause said second lever to move with saidfirst lever, one of said abutments comprising an arcuate spring stripcarried at one endtby. a member rotatable on one of said levers on-an axis .normal to and spaced from the axis of said levers, means. for adjusting the axial deflection of the other end of said'strip, and'cooperating indicia of condition value on said one lever and said strip to indicate operating differentials in accordance with the angular adjustment of said member and said strip.

8; A control device comprising, first and second coaxiallypivoted levers, condition sensing means acting on said first lever to position said lever in accordance with condition value, a control element actuated between two operative positions by said second lever, cooperating abutmentS. on. said levers tocause said second lever to move with saidifirst lever, one of said abutments including a member rotatableion one lever on an axis normal to and spacedfromthe lever axis-and an arcuate strip carried at. one endonnsaid member, a screw adjustable in said member andengagingtthe other end of saidstrip to determinev the relative, axial deflection of the two ends. of said :strip, and cooperating indicia .of condition .value ,on, said; member: and, on said lever.

9. A control device comprising, first and second coaxially pivoted levers, condition sensing means acting on said first lever to position said lever in accordance with condition value, a control element actuated between two operative positions by said second lever, cooperating abutments on said levers to cause said second lever to move with said first lever, one of said abutments being an arcuate spring strip rotatably mounted on one of said levers, means for adjusting the relative axial spacing of the two ends of said strip, and cooperating indicia of condition value on said lever and on said strip.

10. A control device comprising, a frame, first and second levers coaxially pivoted on said frame, an expansible chamber acting on said first lever, a spring acting between said frame and said first lever to oppose expansion of said chamber, indicia associated with said spring to indicate the control point of the device in terms of condition value, a snap switch actuated by said second lever,

cooperating abutments on said levers to cause said second lever to move with said first lever, one of said abutments being an arcuate spring strip rotatably mounted on one of said levers, means for adjusting the relative axial spacing of the two ends of said strip and cooperating indicia of condition value on said lever and on said srtip.

References Cited in the file of this patent UNITED STATES PATENTS 

